Valve assemblies play a very important role in the automatic control of modernized factories. Factory production depends on the correct distribution and control of flowing medium. Regardless of energy exchange, pressure decrease or simple container charging, the control needs to be completed by final control elements, and especially, valve assemblies are the most commonly used type of the final control elements. Valve assemblies which are used for adjusting pressure parameters adjust the set values of the pressure by changing the compression amounts of the springs via valves to stabilize the pressure of fluid within the needed pressure range. As shown in FIG. 1, the working principle is that a signal pipe 101 needs to be connected to a pressure tapping point to be sensed and controlled, an actuator 102 is enabled to sense the pressure of the pressure tapping point, and when the force produced when the pressure of the pressure tapping point acts on the lower part of a diaphragm 105 is larger than the force of a main spring 106, the diaphragm 105 moves upwards to drive a valve stem 107 and a piston 108 to move upwards and the piston 108 leaves a valve port to realize a pressure regulator opening action. When the pressure of the pressure tapping point is smaller than the force of the main spring, the piston moves downwards to be in contact with the valve port 109 to realize the goal of closing, wherein the closing force is fully provided by the main spring 106.
During the realization of the present invention, the inventor finds that the prior art at least has the following problems: when the force of the main spring is too large, although a lower limiting block 110 limits the downward stroke of the valve stem 107, due to accumulation of various errors, the limiting block 110 cannot play a very good limiting role. The force of the main spring is still transferred to and concentrated on a valve core assembly (valve stem 107, piston 108 and valve port 109). For this reason, the valve core assembly can be damaged, the valve may not to work normally and unnecessary losses are caused.